Wcdma Uplink Synchronization Tracking Algorithm

To despread and demodulate the signal correctly in the spread spectrum system, the PN code phase of the receiver must be synchronized with that of the input signal precisely. Multipath channel exists in the wireless environment for radio signal reflection by obstacles between transmitters and receivers. Because of the different time delay among multi-paths, the received signal undergoes frequency-selective fading. However, multipath components can be resolvable due to the autocorrelation of the spread spectrum signal, thus the optimal receiver equals coherent RAKE reception, i.e. maximum ratio combining the independent components which endure flat fading or frequency non-selective fading. Synchronization of PN code and separation of resolvable multipath components need to estimate the exact time delay among the multipath components. So multipath acquisition and code tracking are utilized. Multipath acquisition decide the coarse PN code phase and pick up the available multipath components. Following, code tracking confirm the PN code phase precisely and track every multipath component's delay drifting due to Doppler effect.In this paper, the code tracking technique in spread spectrum communication is introduced. And the PN code tracking scheme adequate for the WCDMA uplink is presented and combined with the mulipath acquisition and channel estimation algorithms to complete the RAKE receiver scheme. Computer simulations show the tracking scheme meets the requirement of WCDMA uplink in 3GPP protocols and has good performance. Meanwhile, potential of the scheme is indicated.